However, they said that policy is at odds with the Immigration and National Act (INA), which requires U.S. officials to assess whether immigrants are likely to become a "public charge" that need federal assistance. In those cases, the government is not supposed to allow those people to enter the country.

"We were thus shocked to discover that both the State Department and DHS exclude reliance on almost all governmental welfare programs when evaluating whether an alien is likely to become a public charge," they wrote. The letter said government only examines likely reliance on Supplemental Security Income and the Temporary Assistance for Needy families (TANF) programs, just two of 80 federal assistance programs.

As a result, the senators asked for an explanation of why this policy is not being implemented correctly, and how many visa applications might have been denied over the last decade if the policy were followed according to the INA. It also asked how many immigrants were turned away due to assessments that they would become public charges, and how many immigrants that entered the U.S. have become public charges.

The senators asked for answers by Aug. 20. The senators who authored the letter are the ranking members of the Budget, Judiciary, Finance and Agriculture committees.